How were the Assyrians able to build such good cities and roads?

A lot of the information available suggests that the Assyrians managed to build better cities and roads because they had a solid leadership with a clear vision for the empire. Their leadership managed to establish a strong military that ensured that the empire and its cities were well protected. The administration allowed the people some level of freedom and ensured that the empire remained stable with minimal upheavals from within.  With such an environment, the Assyrians managed to focus on development and prosperity.
The king needed an elaborate road network and infrastructure to ease administration of the expansive territory. Thus, he invested in building good roads and good road stations that enhanced communication between the different towns and the central command located in the main city. Enhanced infrastructure and communication improved administration and provided an opportunity for the growth and development of good cities, which enjoyed a stable environment and resources.
https://www.britannica.com/place/Assyria

https://www.ucl.ac.uk/sargon/essentials/governors/thekingsroad/